Glycans are often functional determinants of biological events of immunoglobulin G (IgG), as IgG recognizes and clears pathogens and toxins through coupling specificity of variable region to Fc-mediated cellular functions that are regulated by modulating the composition of the Fc-linked glycans (Maverakis E, et al (2015) J Autoimmun 57 (6): 1-13.). In particular, close association between variations in the glycosylation of IgG and changes in the immune status of humans have long been appreciated, facilitating glycoforms of IgG as molecular signatures for the diagnosis of various diseases like rheumatoid arthritis (RA) and prediction of immune responses. According to Gao et al. (Characterization of glycosylation profiles of HIV-1 transmitted/founder envelopes by mass spectrometry. J Virol. 2011; 85(16):8270-84.), “because of the complexity of samples, wide dynamic range of glycopeptide concentrations, and glycosylation heterogeneity, it is a great challenge to successfully complete glycosylation analysis.” Yet, many trace N-glycans are biologically important, e.g., acidic N-glycans with anionic residues, such as sialic acid, sulfate, and phosphate groups. For example, IgGs with sialic acid-terminated N-glycans exhibit anti-inflammatory activities (Anthony R M, et al (2008) Science 320 (5874):373-6). Sulfated glycoproteins are important for biomarker discovery, as well as investigating molecular recognition processes. Therefore, a comprehensive glycomic approach that accounts for low-abundance and difficult-to-detect, but biologically important, species is highly desired.